Technology is already known that, in a case where a cylinder pressure sensor provided in an internal combustion engine is causing a sensitivity decrease, determines whether the sensitivity decrease is due to a failure of the cylinder pressure sensor or is due to the adherence of deposits to the cylinder pressure sensor. For example, in Japanese Patent Laid-Open No. 2013-044258, technology is disclosed that determines the adherence of deposits based on the number of occurrences of pre-ignition. The aforementioned technology employs a technique that measures the number of occurrences of pre-ignition within a fixed period after pre-ignition has been intentionally caused to occur, and compares the number of occurrences with a previously set determination frequency. The reason the number of occurrences of pre-ignition is used as an index for determining adherence of deposits is described hereunder.
Once pre-ignition occurs in an internal combustion engine, deposits that are detached by the impact generated by the pre-ignition serve as ignition sources, and pre-ignition occurs in a chain-like manner. Therefore, if there are a large number of occurrences of pre-ignition within a fixed period, it can be said that deposits of an amount corresponding thereto are adhered.